Electronic digital computing devices



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READ wzmz OUTPUT IN DUT 3,012,725 Patented Dec. 12, 1961 3,012,725 ELECTRONIC DIGITAL COMPUTING DEVICES Frederic Calland Williams, Romiley, Tom Kilburn, Davyhulme, Manchester, and Geoffrey Colin Tootill, Hawley, Camberley, England, assignors, by mesne assignments, to International Business Machines Corporation, New York, N.Y., a corporation of New York Original application .lune l, 1950, Ser. No. 165,434, now Patent No. 2,810,516, dated Oct. 22, 1957. Divided and this application July 22, 1957, Ser. No. 673,524 Claims priority, application Great Britain .lune 22, 1949 23 Claims. (Cl. 23S-157) This invention relates to electronic digital computing machines and is particularly, although by no means exclusively, concerned with binary-digital computing systems which employ digital storage or memory devices of the type described in the paper by F. C. Williams and T. Kilburn, Proc. Institution of Electrical Engineers, part III, March 1949, pages 81-100.

This application is a divisional application from application Serial No. 165,434, led June l, 1950, now Patent No. 2,810,516, by F. C. Williams et al., for Electronic Digital Computing Devices.

Universal digital computing machines, i.e. computing machines which are intrinsically capable of performing any computation desired, provided that adequate storage is provided, operate by handling a mathematical problem as a series of simple arithmetic operations which can be performed upon numbers which are held in a storage or memory" within the machine. Such machines, in general, conform to a similar pattern. In these machines there exists a store in which all data required in the solution of a problem is recorded, each element of data having unique location or address defined by its spatial or temporal position or by a combination of both, one or more arithmetic organs, which generally include a subsidiary store or accumulator, in which elementary arithmetical operations can be performed between numbers fed (generally at different times) to the arithmetic organ, and finally a control system which controls the sequence of operations of the machine and orders the necessary transfers of numbers and arithmetical operations.

For any particular problem the programme of operations to be carried out by the machine is broken down into a series of orders, each of which represents an elementary number transfer or arithmetical operation. These orders may be conveniently expressed in code form as numbers and stored in the memory of the computing machine, as part of the data of the problem, until required and called into operation by the control system of the machine. Each step of operation performed by the machine in response to a single order may be reduced in effect to the transfer of a number between the store and some other portion of the machine (in general the arithmetic organ) and an arithmetical operation may or may not occur automatically as a result of the transfer. For example, two numbers may be added by first feeding one number from the store to the arithmetic organ, where it is stored in an accumulator, as a result of a first order or instruction and then feeding the second number from the store to the arithmetic organ, under the control of a second instruction, in such a fashion that it is added to the first number held in the accumulator. The coded order or instruction words therefore have to define the addresses in the main store of the machine from which or to which a number transfer is to occur and must also define the other destination or source of the transferred number and any arithmetical operation which is to occur as a result of the transference.

The obeying of each single instruction by the machine may be regarded as the fundamental unit of opera tion of the machine and the interval involved in the obeying of an instruction is referred to hereinafter as a ban A sub-interval or, as it is sometimes referred to, a minor cycle is occupied by the time taken to express within the machine in dynamic form a number or instruction word. Such intervals are referred to as beats It is apparent that any number transference must by itself occupy one beat as, in order to transfer a number or word which exists in static form in the store to another address Where it is again represented in static form, it is necessary to convert the number or word to dynamic form and that such conversion is the essence of the transfer as any digit of a number or word existing transiently in dynamic form may be employed to recreate its static counterpart immediately in a storage location.

In working through a problem the computing machine normally obeys instructions sequentially and as the instruction words are stored in the main storage system of the machine each instruction word has to be read out in turn in dynamic form, the process of reading involving the transient identification of each digit of a word held in a store and the simultaneous provision of a transient signal representative of the digit, so that the word may effect the necessary control functions in the machine which are requisite for the obeying of the instruction. The sequential selection of instruction words from the store must be performed by a subsidiary controlling function of the machine; the utilization of each instruction word in the store necessarily involves in effect a transfer of that word out of the store and may be effected under the direction of a control instruction which is held in a subsidiary storage portion of the machine. It is arranged that upon the completion of the operation of obeying each instruction, the control instruction relating to the next instruction in the sequence to be obeyed is caused to become effective and initiate the events occupying the next bar in the operation of the machine. The control instructions required when instructions recorded in specified addresses in the store are to be selected sequentially may be readily derived, for example, by the operation of a completion signal at the end of each bar.

The automatic process of sequential selection of nstructions may require to be broken automatically in certain circumstances. For example, transfer of the control exercised by the control instructions may be required to take place in response to an arbitrary instruction in the sequence, possibly a reversion to an instruction previously used or a jump ahead to a new instruction. Such transfers of control may occur as the result of a test made upon the state of a partial solution existing in the computing machine and the conditional transfer may be produced by appropriate arrangement of the instructions recorded in the store when the programme for the problem on hand was designed. For example, a particular group of q instructions whose addresses may be denoted as n+1, n-f-Z n-l-q-l, n-i-q may be repeated if, at a particular stage in the solution of a problem the partial solution available complies with a certain requirement (e.g. of sign), while if the requirement is not complied with the machine may be required to progress to a new set of instructions. Such a conditional transfer of the control of the machine may be effected by arranging that instruction n+q-1 calls for the necessary test of the partial solution and that when instruction n-l-q-l has been obeyed, causing the machine to proceed either to instruction n-f-q, or by omitting one instruction, to instruction n-l-q-i-l in dependence upon the result of the test. Instruction n-l-q may be designed to cause a backward transfer of control by causing the machine to subtract a quantity q from the control instruction number, the number q being obtained from the store wherein it was originally loaded as part of the data, so that the control instruction reverts to instruction n. The instruction n-l-q-l-l on the other hand may be designed to allow the solution to proceed. Other arrangements may be made for control transfer; for example, an instruction n, selected by the control instruction after an instruction calling for a test has been completed, may require control to be transferred to an entirely new instruction in address location m and this may be achieved by causing the instruction n to replace the control instruction by a number m-l so that the normal sequential selection function performed by the control instruction mechanism causes the instruction m to be next selected. Alternatively, the instruction n may be designed to cause the number (m-U-n to be added to the existing control instruction number with the same effect.

One existing form of computing machine of the general type outlined above comprises a memory, referred to as the Main Store, which consists of a number of cathode ray tube storage units operating upon the principles described in the aforesaid paper by F. C. Williams and T. Kilburn. The machine operates in the serial mode, i.e. numbers in binary notation are represented dynamically as trains of pulses in common channels and each word occupies an address comprising a line or portion of a line on one cathode ray tube of a raster-like pattern applied in common to all the cathode ray tubes in the store. Reading of a particular word in the store, i.e. the observation and reproduction in dynamic form of that word during one beat without destruction of the recorded word may be `achieved by scanning of the appropriate address line in the appropriate cathode ray tube of the store. As explained in the aforesaid paper by F. C. Williams and T. Kilburn, the cathode ray tube store systems require for their operation that all the recorded information should be periodically regenerated, and this may be most conveniently carried out by arranging that sequential regeneration takes place during alternate, or so called scam beats according to a cyclic pattern while during intervening or so called action, beats selected addresses are made active," i.e. the contents of single selected address are made available for reading.

The mode of operation of the storage system with such interlaced scan and action beats, when taken in conjunction with the provision of a main store in which both data and instruction words are initially recorded, results in a rhythm of operation for the machine in which each bar normally comprises four beats. The above-mentioned existing machine, in order to operate in this rhythm, comprises in addition to the main store referred to above and an arithmetic organ, two subsidiary stores which perform the controlling function for the machine. These stores, each of which is of the cathode ray tube type, each has a capacity of one word and the first, which was known as the control register, recorded a number which is referred to in this specification as the control instruction and which is effectively a number defining the address in the main store of an instruction which is being currently obeyed, while the second store, which was known as the current instruction store, acts as an intermediate repository for each current instruction word" read from the Main Store before that instruction word is fed to perform its address selection and controlling functions. In simple operation during the first (Scan l) beat of a bar the control instruction number (n) is caused to be increased by one, by means of a suitable adding circuit associated with the regenerative loop of the control register store, and the number n-l-l, which is simultaneously read out, performs the selection of the address in the main store of the next instruction to be obeyed. During the next (Action 1) beat the selected instruction word is read out of the Main Store and written into the current instruction store where it is held until the next (Scan 2) beat when it is read out of this subsidiary store and fed to the address selection and routing control mechanism to prepare the source and destination and direction of transfer which will be involved in the word transfer comprised in the obeying of the instruction in the next beat. During the fourth (Action 2) beat the instruction will be obeyed, a number or instruction word being transferred between an address in the Main Store and some other part of the machine (generally the arithmetic organ when a number is being transferred, but possibly the control register if a control transfer is being effected) and will generally be completed in the single beat. If, however, the instruction is one which calls for an arithmetic operation occupying more than one beat then provision is made for holding up the initiation of the next bar until the scan beat following the beat in which the completion of instruction occurs. In the aforesaid existing machine it was assumed that the instruction words represented in a coded form the address in the Main Store and the address in the arithmetic organ (or elsewhere) between which a number transfer was to be effected and that one digit of the instruction word defined the direction in which the transfer was to occur.

The object of the present invention is to provide an improved computing machine similar in general principle to such existing machine previously referred to in which economy of apparatus, increased facilities of operation and enhanced operating speed may be achieved.

According to one feature of the invention the machine comprises a main storage device for recording both number and instruction data to be employed in the solution of a problem, an arithmetical organ for performing a chosen operation upon or between numbers or words fed thereto from said main storage device and a control system including means for storing and utilising a control instruction word and means for storing and utilising a particular or present instruction word selected and transferred from said main storage device under the control of said control instruction word characterized in that the storage of both said control instruction word and said present instruction word are effected within a single storage unit.

According to another feature of the invention the selection of the desired data from the main storage device and the controlling of the subsequent operation to be performed therewith within the machine are effected through the intermediary of different digit portions of a common instruction word.

According to a further feature of the invention the machine is provided with means for testing a partial solution and, in accordance with the result of such test, electing conditional transfer of the control of instruction word selection to one or more different instruction words.

As already explained, machines of the general form described normally operate in a rhythm of four beats to a bar but in accordance with yet a further feature of the invention a second storage device is provided for recording instruction Words and the operation of the machine then arranged to take place in a bar consisting of two beats only during the first of which a chosen instruction word is read out from said second storage device and is used to prepare means for selecting a data item from the first or main storage device and to prepare means for performing the required arithmetical or other operation while during the second beat such operations upon said data are obeyed whilst the control means simultaneously select the next instruction word in the second storage device in readiness for the next following operation. Such feature of the invention is particularly adapted for use with storage devices which require repeated regeneration of the data held therein in which case the respective regeneration or scan beats and the operative or action beats of the first and second storage devices are interleaved so that the instruction storage device performs an action 

